The present invention relates to internal safety valves for fluid containment vessels. It also relates to positive displacement metering pumps for fluid transport vessels.
Society today requires that numerous chemical materials be handled, many of which have hazardous or obnoxious properties. These materials include acids, alkalies, chlorine, ammonia, liquefied petroleum gases, hydrogen sulfide, hydrogen cyanide, sulfur dioxide, mercaptans, fuels, pesticides, radioactive materials, and industrial wastes. To insure that these hazardous, obnoxious, or valuable or sensitive materials do not escape into the environment during their processing, storage and transportation they must be contained in strong vessels or piping systems. These vessels and piping systems must not only provide satisfactory access to the contained materials, but must completely and safely contain them at all times when the escape thereof to the outside environment is unsafe or otherwise undesirable. In some cases, it Is even desirable to protect the material itself from the environment.
The unintentional escape of such substances f rom their containers can have disastrous consequences, including the loss of life, damage to health or property, public inconvenience and even the mass evacuation of public areas. Accordingly, there is a strong need to provide safer containment systems. Although totally sealed vessels providing no access to the outside can be designed to be highly reliable, access to the materials stored in them is of course necessary. Valves with or without mechanical actuator devices to operate them are therefore provided. The containment vessels are typically reliably built, and it is the traditional valvings thereof which are the weak points in the system and thereby reduce the reliability and usefulness of the entire containment system.
In some instances, relatively large leaks or seepage rates from valves are tolerated by users and by society depending upon the particular location and the state, pressure and properties of the stored materials whether hazardous or nonhazardous. However, in the case of extremely toxic, reactive, obnoxious, valuable or sensitive materials even small failures of containment or seepages can be so objectionable as to discourage or even preclude the handling, transportation or storage of them. This problem is growing due to the public's increasing anxiety over the handling of chemical and radioactive materials by both industry and government. Materials which exist in normal conditions as high pressure or liquefied gases are particularly troublesome especially if the materials have a foul odor or corrosive properties. Seepages may not even approach hazardous levels before the users of the materials are exposed to adverse publicity, litigation and extremely stringent and costly regulations. When valve systems used with hazardous, obnoxious or valuable materials fail, the release of the materials can thus have potentially lethal and costly consequences. This failure can result from highway accidents, fires, explosions, earthquakes, storms, misuse, abuse and vandalism.
Known valve systems typically comprise a moveable plug assembly or port which can be manipulated relative to a valve seat to open or close the valve. This manipulation is usually done by transferring a mechanical force from outside of the valve to the plug or seat by means of a valve stem passing through a packing gland or a mechanical seal. These seals or glands are dependent upon tight mechanical closures, and they invariably leak to some measurable extent. These valves also are subject to relatively rapid friction wear causing the seals thereof to ultimately fail. Another known valve apparatus is that disclosed in U.S. Pat. No. 4,872,640. The entire contents of that patent, of each of the references cited therein and any other patents mentioned anywhere in this disclosure are hereby incorporated by reference.
Most known valves are designed such that if they are to be operated in response to instrumentation or personnel, they must be installed outside of their containment vessel, usually on a nozzle or an attached pipe. While the valve body itself might be capable of withstanding external exposure to the contained material, the operators extant cannot withstand such materials or hard pressure. They characteristically are designed to operate in gentle conditions of temperature, pressure and atmosphere. Accordingly, valves and valve actuators are now usually placed outside of the containment vessel, accessible to personnel. This positioning means, however, that the valve is relatively vulnerable to mechanical damage and damage by impacts, fires, abuse and so forth which would not necessarily damage the containment vessel itself. Further examples of valves positioned generally inside of fluid vessels include those shown in U.S. Pat. Nos. 1,474,297, 3,164,358, 3,199,534, 3,388,719, 3,986,525 and 4,280,679.
To make the valves less vulnerable and more resistant to some types of external hazards, such as fire, protective shielding is sometimes used. Its use is generally limited, however, and for transportation vessels, it typically increases the vehicle's weight unacceptably.
Specialized internal excess flow valves have been designed to at least partially remedy this vulnerability problem. These valves close automatically using the system or product pressure at preset flow rates. They do not communicate with the outside environment and cannot be controlled externally. By necessity they are designed not to close unless the rate of flow exceeds the maximum expected flow requirements of the system. They are not adjustable as to response without entry into the vessel. Unfortunately, the nonadjustability of these valves and the need to set a flow level higher than the maximum expected flow limits their usefulness. Further, unintentional escapes of material through leaky or partially broken external systems can result in dangerous or obnoxious releases to the environment at flow rates considerably less than the maximum expected flow rates. As a result, these valves protect only against unlikely circumstances involving total downstream failure.
The vulnerability problem has been addressed in a few cases by installing the seat and plug portions of the valve within the tank or vessel envelope and placing the mechanical linkage on the outside of the tank envelope. These valves have shaft or stem seals outside of the tank envelope, and they are vulnerable to physical impact as well as to stem seal seepage. The theory is that the external portions of the valve can be broken or shorn off in an accident and the internal plug and seat will remain intact. This is unlikely however due the actual mechanical stem linkage of the external system to the internal system. Furthermore, in actual practice, this mounting arrangement is easily damaged when impacted, leaving the system totally unprotected and apt to leak.
The seal or gland leakage problem has been partially addressed in some known devices by using bellows or diaphragm seals on the stems of otherwise conventional valves, or by using magnetically-transparent rigid seals through which magnetic forces are transmitted to mechanically manipulate the valve plug or seal; these valves are generally referred to as electromagnetic solenoid valves. In the case of the bellows or diaphragm seal, the seals are intrinsically weak to accommodate the low forces provided by conventional valve actuators and intrinsically small to fit into conventional valve geometries. They are therefore subject to damage by relatively small forces and cannot withstand the environmental rigors inside containment vessels.
Electromagnetic solenoid valves are limited to small sizes and low pressure operating ranges due to the practical limitations on the power or force output of reasonably small magnetic actuators. These devices attempt to solve the problem of limited force by means of pilot valves. The ports of these pilot devices though are very susceptible to plugging with foreign matter and require that the fluid being contained have a minimum pressure differential relative to the downstream pressure in order for the valve to move or even to reliably stay in one position. Electromagnetically generated forces, furthermore, utilize electric currents sufficient to generate sparks, and therefore are often not suitable for use around flammable or explosive mixtures. No known devices of this type have the stated ability to operate within high pressures or the high pressure containment vessel itself.
Valves which are to be operated or controlled from the outside of the vessel are typically designed to be installed outside of the vessel in whole or in significant part as previously stated. This leaves the valve highly vulnerable to accidental damage and susceptible to seal leakage particularly for high pressure systems. A practical solution to the problem of externally controlling the action of a valve when the valve is fully contained within a pressure vessel in a manner which prevents even seepage leaks from the control device itself was not previously known.